Conventionally, the linear motion guide unit is constituted in a fashion a slider is allowed to travel along an elongated guide rail through more than one rolling element. The recently remarkable development in mechanical engineering technology call for various sorts of linear motion guide units, especially, linear motion guide units of the type using a rolling element of cylindrical roller, which will carry heavy loads even though miniature in dimension. Advanced linear motion guide units are used in any relatively sliding components in machinery as diverse as semiconductor fabricating equipment, machine tools, assembling machines, conveyers, and so on, and further expected to find more extensive application to various sort of machinery. The linear motion guide units designed especially to work on semiconductor fabricating equipment, measurement/inspection instruments, and so on are needed to meet all the duties of micromechanical construction, high-speed sliding performance, high mechanical stiffness, and high accuracy while getting smaller and smaller in construction. Rollers in the linear motion guide units are expected to roll through a circulating circuit composed of a load-carrying race defined between a guide rail and a slider, a return passage made in the slider, and turnaround passages made in the slider to communicate the load-carrying race and the associated non-loaded return passage with each other.
In the commonly assigned Japanese Patent Laid-Open No. H07-91446, there is disclosed a linear motion guide unit in which a retainer means to keep more than one rolling element of cylinder, or roller, is held in place by means of just snap-fit operation and serves to increase permissible load rating. The retainer means is composed of a retainer plate to support the rollers and a holder band coming into engagement with the retainer plate to fasten the retainer plate to a carriage of a slider. The retainer plate may be fastened to the carriage with certainty and ease after the holder band has just snap-fit into the carriage. With the linear motion guide unit constructed as stated earlier, the retainer plate is placed to extend between the upside and downside load-carrying races made on the carriage. The holder band has a major portion to fit into a lengthwise recess made through the retainer plate and forward and aft end caps and lengthwise opposite bent ends to come into snap-engagement with their associated holes in the end caps. After the retainer means has been incorporated into the slider, the rollers are held in the load-carrying races defined between the guide rail and the carriage of the slider.
Another linear rolling guide system is disclosed Japanese Patent Laid-Open No. 2002-5162 in which joint construction between leading and trailing guide rail sections is especially designed to relieve severe concentration of stress at the butting construction against each other and further keep the rollers against getting caught or falling in any gap left between adjoining guide rail sections, making sure of smooth transfer of the rollers from any one of the guide rail sections to the other. The linear motion guide system is comprised of the guide rail having lengthwise load-carrying races, a sliding carriage fitting over the guide rail in a way traveling relative to the guide rail, and many rollers rolling through an endless circulating circuit. The guide rail is constructed with guide rail sections lined up end-to-end. The joint where the adjacent guide rail sections are butted each other is oriented to intersect with the rotational axes of the rollers running through the load-carrying races.
A further another sort of linear motion guide means is disclosed in Japanese Patent Laid-Open No. 2004-144146, which is envisaged getting the number of gaps in an endless circulating circuit, which might cause any resistance that is encountered when a retainer runs through there, as less as possible, making sure of not only smooth traveling of the retainer, but also smooth circulation of the rollers. With the linear motion guide means constructed as stated earlier, a carriage that fits over or conforms to a guide rail to move relatively to the guide rail is made therein with the endless circulating circuit made up of a load-carrying race, a non-loaded return passage extending in parallel with the load-carrying race and a pair of non-loaded turnaround passages to communicate the load-carrying race and the return passage with each other. The rollers inside the endless circulating circuit are held in the retainer to roll and run sequentially. The endless circulating circuit is made throughout with a lengthwise recess in which there is snugly accommodated guide members having guiding area to control the movement of a connecting band to keep the retainers at desired intervals.
The recent linear motion guide units, even though more miniature in construction, are needed to extensively meet all the duties of high-speed sliding performance, high mechanical stiffness, and high accuracy. There is a major challenge about how the miniature linear motion guide units using small rollers as the rolling elements are applied to extensively various types of machinery. To cope with this, it is very critical to make certain of smooth rolling of the rollers throughout the entire circulating circuit in the linear motion guide unit. In particular, when using the miniature rollers or needles, it is severe to make the rollers roll or tread without any obstacle across boundary lines in the circulating circuit, especially, a boundary between the load-carrying race and the associated turnaround passage. Moreover, it is inevitable to guide the rollers with smooth but no tilt.
In the linear motion guide units in which the small rollers or needles are selected as rolling elements, alignment problems to guide rollers in good rolling order without leaning in rolling posture are more encountered, compared with the construction using balls. The prior linear motion guide units as recited earlier can be, to some extent, applied to comparatively small rollers, nevertheless, miniature rollers extremely small in size, for example rollers of 1 mm or so in diameter, poses a new challenge whether they are allowed to roll orderly and smoothly without encountering any obstacle when rolling across boundaries where parts or members including end caps, carriage, retainer plates, and so on abut against one another in the endless circulating circuit. As opposed to the linear motion guide units using the balls as the rolling elements, the rollers or needles have to be guided not only on their circular surfaces, but also on their axially opposite end surfaces to run through the circulating circuit without leaning in rolling posture with respect to the running direction. As for the miniature rollers, even a tiny gap at a boundary between butting members could cause any obstacle to rolling movement of the rollers. This means there is a significant challenge to ensure smooth, steady rolling motion of the miniature rollers.
With the prior linear motion guide units, the boundary 28 between the retainer plate 13 and the leading edge 29 of the end cap 4, as shown in FIG. 13, is largely beveled or chamfered at 35. The roller 5 collides readily against the bevel edge 35 to get caught at the associated circular corner. The trapped roller 5 eventually contorts the leading edge 29 of the end cap 4, which is thin in thickness, into the damage and interferes with smooth rolling of subsequent rollers. It is moreover to be understood that the boundary 28 in the circulating circuit normally conforms to a specific location where the end cap 4 butts against the edge 34 of the carriage 3, or the turnaround passage 30 of the end cap 4 and the raceway surface 12, that is, the load-carrying race 20 of the carriage 3 join together so that the roller 5 will tend to lean to any lopsided posture. Thus, there is a question how the roller 5 rolls with no obstacle across the boundary between members butting together.